In many geodetic applications, methods and systems for attitude determination, i.e. for position and/or orientation determination, of an instrument used are employed. From a position determined using such a system, further measurements which are linked to the position and generally also require a knowledge of the orientation of the measuring instrument in space are then carried out. In principle, the orientation of the instrument can also be derived from the position determination of two or more points. For measuring applications, the 6 degrees of freedom of the handheld measuring instrument, but at least the position and hence 3 degrees of freedom, have to be determined for unambiguously fixing the absolute attitude. The problem therefore consists in the determination of position and orientation as two objects which in principle are achievable separately from one another but must be carried out with linkage for many applications. As a rule, both position and orientation of a generally hand-held measuring instrument are therefore required.
Methods and systems for determining the attitude of objects are required in many kinds of applications. Thus, for example, in geodetic applications, attitude information of a measuring instrument is often used, for example for incorporation of the measuring instrument into a ground coordinate system by measurement. From such a measuring instrument, further measurements are then generally carried out and linked to the attitude information. Another field of use is an automatic machine control, where the attitude of moving vehicles must be known as a basis of control. An attitude determination system for fixing the attitude of moving objects is also required in the marking of sports fields.
Known methods or systems for position determination are, for example, global position determination systems, such as GPS. Assuming undisturbed satellite reception, which is not always guaranteed, for example between rows of houses, in sports stadia, in building trenches or in mining, the position of an object can be determined by means of a GPS transmitter on the object. For fixing the orientation of the object, an additional orientation meter is required. The accuracy of the position data determined from GPS signals is, however, limited—particularly with regard to the height of an object—and is insufficient for many applications. Furthermore, the systems are increasingly inaccurate for moving objects or require greater complexity in the measurement.
Another frequently used method is position determination using tachometers or total stations. In particular, for position determination of moving objects, too, many kinds of embodiments of such systems are present in the prior art for automatic target tracking and surveying of moving objects. As a rule, only one position determination of the object moving independently of the total station is effected here. For determination of the orientation of the object, further measurements to the object can be carried out, for example by means of tilt sensors and a compass.
Other approaches for local positioning systems are based on passive points of known positions. Thus, for example, PCT/EP2004/010571 discloses a system for determining the actual position of a measuring instrument, in which at least two reference points located in a spatial segment scanned by a laser beam are detected and are measured with regard to their distance and their angle of inclination. From the known positions of these detectable reference points and the coordinated distances and angles of inclination, the actual position of the measuring instrument can be derived. The detection, tracking and measurement of the reference points is carried out in an automated procedure by the measuring instrument, the measuring instrument and specially formed elements coordinated with the reference points forming a local position and/or orientation measuring system. In this system, however the reference points must be actively scanned and illuminated using a laser beam, so that the receiving component in the measuring instrument requires a very complex design.
This type of position determination requires reference points which either have to be provided or must already be present. However, this precondition is often not met in open terrain—such as, for example, on sports fields or sports grounds. The erection of, for example, reflector staffs as reference points and the transport thereof make the method complicated.
Another approach for determining the attitude of a moveable unit comprises, in a first step, positioning a scanning unit, preferably a laser scanner, in a location suitable for a measurement to the unit, this location being known or being measured beforehand so that the position of the scanning unit is determined. A measurement of the position of the scanning unit can be effected using generally known methods of surveying technology, for example by means of a total positioning system or of a global positioning system. The scanning unit can, however, also be positioned and measured relative to a predetermined starting point. A measurement by means of the scanning unit is effected therewith from a position of known local or global coordinates.
A scanning unit of the generic type has a radiation source for emitting a laser beam or laser pulse, with which laser beam a solid angle region is scanned. Depending on the specifically chosen realisation of an embodiment, various scanning movements—among the prior art—can be chosen for the spatial segment.
Measured targets present in the spatial section scanned partly reflect the scanning radiation back to the scanning unit, by which the reflected radiation is received and evaluated—with regard to the distance to the measured target and the horizontal and/or vertical angle between an axis of the scanning unit and the measured target. The measured targets are generally distinguishable from the background on the basis of their reflectivity, so that they are recognised simply from the variation in the intensity of the reflected radiation. In addition, further measures for target detection or for automated surveying can also be used. The distance to a measured target detected during scanning of the solid angle region is measured by means of the scanning unit via the radiation reflected by the measured target, preferably by the phase measurement principle or the principle of pulse transit time measurement. Together with the angle information of the emitted radiation, the spatial position of the respective impingement site can be determined in relation to the scanning unit.
The angles to be determined depend here on the specific situation and the specified constraints. If, for example, a measurement is effected only in one plane, it is sufficient to determine the angle or angle component lying in this plane. In the general case, however, a distance and two angles are required for a position determination.
The position information about an object as a measured target or an object equipped with a reflective measured target is therefore obtained by passing a laser beam over a spatial region and detecting, identifying and measuring measured targets located in the spatial region by means of the scanning unit. If, during scanning of a spatial segment, the scanning unit receives no reflected radiation which can be coordinated with a measured target, a subsequent spatial segment is scanned. This search for the target can be effected, for example, via an automatic target searching device.
The scanning unit can scan one or more measured targets; according to the invention, the measured target of the scanning unit is a receiver or a moveable unit—an object—having a receiver which is formed so that it firstly receives a laser beam emitted by the scanning unit and—at least partly—reflects it back and secondly determines its orientation relative to the laser beam or relative to the angle of incidence of the laser beam. This can be effected in various ways.
The arrangement of the attitude determination system of the generic type, comprising scanning unit, receiver and control unit, is generally chosen so that the axis of rotation of the receiving optical system is vertical and the scanning laser beam of the scanning unit is horizontal relative to a reference plane, e.g. a surface. Preferably, after an initial adjustment, the receiving optical system automatically orients towards the scanning unit. The target search of the scanning unit likewise takes place automatically. For example, it is also possible to use a coarse search run for detecting the receiving optical system, which orients a component of the scanning unit suitable for detecting the receiving optical system so that no interaction with a user is required.
The computing unit can be operated as an external component of the system, for example by a user. However, embodiments comprising a computing unit integrated in the scanning unit or the receiver are also possible. The system is then controlled, for example, automatically from the scanning unit or from the receiver.
A receiver of the generic type is generally indirectly or directly connected in a defined manner to a moveable unit, and the attitude of the unit is thus determinable.
The unit to be surveyed may be, for example, a construction machine. It may also be a surveying instrument, the position and orientation of which are to be determined. A further field of use is the use for all types of marking work. This may be both markings for construction work and on sports grounds. For this purpose, the receiving apparatus is mounted, for example, on a mobile marking device for drawing or spraying lines or two-dimensional drawings, such as coats of arms, symbols or texts.
By means of the orientation determination relative to the beam axis, the receiver or the movable unit can be controlled by moving the radiation with its emission axis virtually as a control beam. For this purpose, the control unit is programmed or its hardware designed so that the deviation of the receiver axis from the emission axis is kept constant or reduced or minimized. Thus, each change of the control beam results in a correction of the attitude of the receiver or of the moveable unit. In a continuous sequence of such corrections, the moveable unit follows the moving control beam.
By guiding the control beam according to a predetermined pattern, the unit can be moved with pinpoint accuracy so that, for example, the surface can be changed with processing components. Thus, for example, figures of any desired shape can be marked as vector graphics on the Earth's surface. This permits, for example, the creation of complex club symbols on sports fields.
US 2003/043362 discloses a six-dimensional laser target tracking system according to the above principle. A tracker as a scanning unit measures the polar coordinates of the target, and the target or the receiver of a moveable unit determines its angle of rotation relative to a mathematical tripod which is defined by the beam direction and the polarization directions. This assumes that the tracker or scanning beam must strike a defined point of the receiver on the moveable unit; every incorrect sighting leads directly to an error in the polar coordinates of the moveable unit as the target to be surveyed. Thus, the laser beam of the transmitter of the scanning unit must accurately strike the entry pupil of the receiver optical system. If this is small or far away, the transmitter must sight very accurately in the sense of a “fine pointing link” in order to establish and to maintain the optical connection, but also in order to restore it after a disturbance. This presents problems particularly if the connecting components transmitter, medium or receiver are not stable relative to one another, either because of vibrations or air turbulence or if abrupt movements of the components break the optical connection, for example during movements over uneven ground. Here, the problems or the probability of the failure increase or increases with increasing distance so that there is also a limit with regard to the maximum realizable useful distance. Moreover, for achieving the required accuracies, the system components have to meet high requirements, in particular with regard to the mechanical system which is used for orientation and tracking and which must permit precise orientation and tracking without delay.